1. Field of the Invention
The present invention relates to a clock generating circuit. More particularly, the present invention relates to a charge pump clock generating circuit and a method thereof in a display.
2. Description of Related Art
In a display driving circuit, for example, the source driver or gate driver in a liquid crystal display, a charge pump circuit is required for generating a non-rated supply voltage which is required by the driving circuit.
Generally speaking, a charge pump needs to receive a clock signal to provide the charge. Taking a source driver as an example, the source driver has two clock signals, one is a dot clock signal and the other one is a horizontal sync signal. The dot clock signal cannot be used by a typical charge pump for the frequency of the dot clock signal is between 10 MHz and a few hundreds MHz and the power devices in the charge pump cannot operate at such high frequency. Besides, if the charge pump is designed to be able to operate at such a high frequency, the dynamic power consumption of the charge pump may be too high.
Generally, a conventional charge pump clock generating circuit generates the clock by divided the frequency of the dot clock through directly sending the dot clock to a frequency divider. FIG. 1 illustrates the clock diagrams of a conventional charge pump clock signal, a horizontal sync signal, a vertical sync signal, and a dot clock signal. In FIG. 1, Hsync represents a horizontal sync signal, Vsync represents a vertical sync signal, DOTCLK represents a dot clock signal, and CPCK1 and CPCK2 represent the charge pump clock signal respectively. In FIG. 1, the charge pump clock signal CPCK1 or CPCK2 do not align with the horizontal sync signal, and which seems not affecting the charge pump. However, a charge pump always produces noises in a driving circuit and accordingly wavy noises are generated on the display. Such noises are caused by the asynchrony between the charge pump clock signal and the horizontal and vertical sync signals.
Accordingly, a charge pump clock generating device is required so that the noises produced by the charge pump can fall evenly within every display sync signal such as the horizontal sync signal.